Methods and apparatus for manufacturing hollow metal castings such as cylinder heads, engine blocks, and the like are well known. Conventional prior art processes for manufacturing aluminum castings typically employ a cast iron "flask-type" mold having the exterior features of the block formed on the interior walls of the mold. A sand core, premolded from a mixture of sand and an organic binder and having interior features of the casting formed on by its exterior surface, is placed within the mold. The mold is then filled with molten alloy.
After the aluminum alloy has solidified, the casting is removed from the mold. Because untreated aluminum alloys may be softer or less strong than desired, it is often necessary to heat treat the casting to strengthen or harden the metal. According to conventional manufacturing processes, before the casting is heat treated, the sand is removed from the interior of the casting. An operator chisels the sand out of the interior of the workpiece with a pneumatic chisel. The casting may then be fed into a "shakeout" system, a vibrating table which agitates the casting to further break up the sand and dislodge it from the interior of the casting. When the sand has been removed, the casting is heat-treated in a conventional manner by heating the casting to a high temperature and then quenching the casting. Optionally, the casting may further be heated at a lower temperature to "age" the aluminum alloy.
If it is then desired to recover the sand removed from the interior of the casting for subsequent reuse, additional steps must be taken to process the sand. The sand removed by chiseling and shaking the casting is fed into a sand burnout unit to burn off the binders.
Prior art processes for manufacturing aluminum alloy castings suffer a number of disadvantages. The steps of removing the sand from the interior of the casting by chiseling and shaking not infrequently result in damage or scarring to the as-then unhardened aluminum alloy. Further, the shakeout process must be carried out manually and is thus labor-intensive, thereby increasing the expense of the manufacturing process. Also, the additional steps required to salvage the sand for reuse are time-consuming and require additional labor and equipment expense. The sand recovery process is costly and presents certain environmental problems concerning the handling of the binder waste products.
Efforts have been made to overcome some of the disadvantages associated with prior art methods and apparatus for sand-casting metal objects. One example is disclosed in U.S. Pat. No. 4,411,709, wherein a method for the manufacture of aluminum alloy castings comprises pouring a molten aluminum alloy into a mold having therein a sand core formed from sand and an organic resin binder. After the alloy solidifies, the casting is shaken or vibrated to destroy the core, and approximately half of the sand used to form the core can readily be removed from the casting. Subsequently, the casting is heated, and the organic resin binder in the remaining portion of the sand core is burned off. The sand is thus unbonded such that about 80% of the remaining sand (approximately 40% of the total core sand) falls from the casting by force of gravity. Thereafter, the casting is quenched in a water bath, and the remaining sand in the casting is removed by flowing water through the casting.
While the method disclosed in the aforementioned U.S. Pat. No. 4.411,709 affords certain benefits over the prior art by eliminating the process of vibrating the sand core from the casting, it still suffers certain disadvantages in that it does not eliminate the requirement for shaking or agitating the casting prior to heat treating, nor does it eliminate the additional processing steps needed to recover the sand for subsequent reuse. The aforementioned patent also does not include an age hardening process for increasing the hardness of the metal. Further, since the method disclosed in the aforementioned U.S. Pat. No. 4,411,709 relies upon force of gravity to remove the sand from the casting, sand will remain on flat and upwardly concave surfaces after the binder has burned off.